The present invention relates to a laser light source of which wavelength is shortened using a second harmonic, sum frequency mixing, difference frequency mixing and which is used with a light source for an optical disc, a laser printer and the like.
As a prior art laser light source, for example, as described in an article in Optics Letters, Vol. 13, No. 10, October 1988, pp. 807-809, there is proposed a coherent light source in which a nonlinear optical crystal KTP (potassium titanate phosphate) is used and a second harmonic generation is utilized. In this article, it is reported that a green light with a wavelength of 532 nm is stably obtained as a second harmonic of a YAG laser, which is end-pumped with a semiconductor laser, from the light source.
When such a coherent light source of a short wavelength type which is relatively miniaturized and is readily handled is, for example, utilized as a light source for an optical disc, it is possible to greatly improve a storage density of information. The reason is that, as well known, the storage density of the optical disc increases inversely as the light spot diameter squared and the light spot diameter decreases in proportion to the wavelength of the light.
Moreover, the coherent light source using the second harmonic is also available for a light source for a laser printer. The reason is that by shortening the wavelength, the spot diameter on a photosensitive drum can be made to be small and the resolution of printing can be improved.